Particle analyzer threshold level control



United States Patent 479,891 a 7 Claims. (Cl. 32471) This'application isa division of application Ser. No. 101,289 filed Apr. 6, 1961, nowabandoned.

This invention relates to a circuit for rapidly and accurately changingthe threshold level of a particle analyzer incorporating threshold leveldetector means for determining whether the size of an electric pulsegenerated by the scanning of a particle exceeds the threshold level.

In many laboratories, technicians of relatively low skill are requiredto operate particle analyzers and make adjustments in their controlsettings even though they do not understand their principles ofoperation and, therefore, the consequences of a mistake. For example,hospital technicians frequently use particle analyzers of the Coultertype to make red blood cell and white blood cell counts. In performingthis analysis, the operator must change the threshold level controlsetting from 35 microns, for red blood cells, to 50 microns, for whiteblood cells, and then back to 35 microns. Obviously such a procedureincreases the probability of obtaining an erroneous analysis.

It is therefore a principal object of this invention to provideeconomical means for rapidly changing the threshold level of a particleanalyzer without affecting its accuracy.

This and other objects and advantages of the inventionwill be moreclearly understood from a detailed description of a preferred embodimentset forth below. The drawings-are primarily diagrammatic and symbolic innature in order to kep the description concise and intelligible, asthose skilled in the art are familiar with many of the specific circuitswhich are suitable for constructing the combinations to be described. v

In the drawings in which like or equivalent'elements have the samereference numerals:

FIG. 1 is a circuit diagram of a preferred embodiment of the inventionincorporated in a Coulter-type particle analyzer adapted for makingblood cell studies.

FIG. 2 is a diagrammatic view of a cathode ray oscilloscope displayshowing two conditions of threshold adjustment capable of being usedwith the circuit of FIG. 1.

The particle analyzer of FIG. 1 comprises a fluid metering apparatus 10,a preamplifier 20, an amplifier 30, a cathode ray oscilloscope 35, athreshold detector circuit 40, a counter gate circuit 60, a counter 65and a control circuit 70.

The fluid metering apparatus 10 is a device for metering a predeterminedamount of fluid having the particles to be analyzed suspended thereinand for generating electrical signal pulses whose parameters arefunctions of the physical properties of the particles that are passedthrough the apparatus or scanned. One such fluid metering apparatus isdescribed and claimed in US. Patent No. 2,869,- 078 and the reader isreferred to that patent for a complete description of its structure andmethod of operation.

The fluid metering apparatus 10 comprises two main sections. The firstis the scanner 11 which contains transducer means for transforminginformation on the physical properties of the particles which arescanned into electrical signals which can be analyzed by electronicdevices. In this preferred embodiment, the scanner is of the Coultertype. Its structure and method of operation are taught in US. Patent No.2,656,508 and the reader is referred to this patent as well as US.Patent No. 2,869,078 where a complete disclosure of the fluid meteringapparatus of the preferred embodiment will be found.

The second section of the fluid metering apparatus is the manometer 15.This section provides signals which indicate the beginning and the endof the period in which a carefully metered volume of fluid is beingscanned.

The scanner signals, which are functions of the physical properties ofthe particles which are scanned, are transmitted by channel 10a to theinput of the preamplifier 20. The manometer signals, which indicate thebeginning and the end of the scanning period, are transmitted to theinput of the control circuit 70 by channel 10b. A control signal whichcauses energizing and de-energizing of the scanner electrodes istransmitted from the control circuit 70 to the scanner 11 by channel70a.

The preamplifier is designed to amplify the weak signals generated bythe scanner and received from channel 10a. Its circuit contains meansfor biasing its active amplifying element to cut-off in response to asignal received from the control circuit 70 through channel 70b at theend of a scanning period. A complete description of the preamplifiercontrol circuit of the preferred embodiment will be found in myco-pending application Ser. No. 479,- 907, filed Aug. 16, 1965 andentitled Particle Analyzer Control Circuit which is also a division ofmy application Ser. No. 101,289.

The signals amplified by the preamplifier 20 are transmitted by channel20a to the input of the amplifier 30.

The amplifier 30 amplifies the relatively low level signals receivedfrom channel 20a to a higher level. These high level signals aretransmitted to the vertical deflection plates of the cathode rayoscilloscope 35 by channel 30a and to the input of the thresholddetector circuit 40 by channel 30b.

The function of the threshold detector circuit 40 is to determine whichsignal pulses received from channel 301) have amplitudes which exceed apredetermined threshold level and to amplify and transmit those pulseswhose amplitudes do exceed the threshold level to other parts of thecircuit for further analysis.

It is taught in the patents previously referred to that the Coulter typetransducer or scanner will generate a signal pulse having an amplitudewhich is a function of the volume of a particle which has been scannedby the transducer. Because the predetermined threshold level is directlyrelated to a respective particle volume, it is possible, by use of meansfor counting the number of pulses which are amplified and transmittedfrom the output of the threshold detector circuit 40, to determine thenumber of particles having volumes in excess of the predetermined size.

The threshold detector circuit 40 comprises an amplifier tube 41connected in a cathode follower configuration to channel 30b through acapacitor 42. The output signals from the cathode follower stage appearacross cathode resistor 43 and the detector portion of the circuit whichcomprises diodes 44 and the threshold level control circuit whichincorporates resistors 45 and 46; potentiometers 47, 48 and 49;rheostats 50 and 51 and switch S-3. Signal pulses having amplitudes inexcess of the predetermined threshold level appear at junction 52 andare amplified by amplifier 53 for transmission to other parts of thecircuit via channel 40a.

The predetermined threshold level signal is obtained by switching thepole of switch 8-3 to the appropriate contact, either R (red bloodcells) or W (white blood cells) in this embodiment. The switch S-3connects junction 52, through the resistor 45, to the slider of eitherthe potentiometer 47 or the potentiometer 48.

The potentiometer 47 is connected in a voltage divider circuit with thepotentiometer 49, the rheostat 50 and the resistor 46 across the outputterminals of a 240 Volt DC.

source. Similarly, the potentiometer 48 is connected in a voltagedivider circuit with the potentiometer 49, the rheostat 51 and theresistor 46 across the output terminals of the source.

Because of this circuit arrangement, a positive potential will appear atthe junction 52. The slider of the potentiometer 49 is adjusted underno-signal conditions so that the base line or reference potentialdeveloped across the cathode resistor 43 is at a proper magnitude, whichis less positive than that appearing across the junction 52 and groundduring quiescent conditions.

In this condition, the diodes 44 are back biased. If a positive signalpulse having an amplitude in excess of the threshold level istransmitted by the channel 301) to the detector circuit 40, the grid oftube 41 will be driven in the positive potential direction, therebyincreasing the cathode current. When the potential at junction 54exceeds the potential at junction 52 by more than the work potential ofthe diodes 44, the diodes will become forward biased and those portionsof the pulse signal envelope having heights in excess of the thresholdlevel will appear at junction 52 and, amplified in level, at channel40a. Pulses having amplitudes which are less than the threshold levelwill not cause the diodes 44 to switch into the conduction state andtherefore will not appear at channel 40a. In this manner, signal pulseshaving amplitudes in excess of the threshold level are detected.

The signal pulses appearing at channel 40a are transmitted to the inputof the counter gate circuit 60. The counter gate circuit performs twofunctions. Its first function is to act as a limiter so as to generateconstant amplitude output pulses in response to input pulses receivedfrom channel 40a. Its second function is to act as a gate so as only totransmit signal pulses to the counter 65 by channel 60a when it receivesthe proper signal from the control circuit 70 via channel 70c. Thecounter gate circuit 60 also transmits pulses to the beam intensitycircuit of the oscilloscope 35 via channel 60b at all times when asignal is received from channel 40a. In this manner a visuallydistinguishable threshold level may be displayed on the oscilloscopescreen. The counter gate circuit is more fully described in mypreviously identified application Ser. No. 479,907.

The counter 65 may be any mechanical, electrical or electro-mechanicalcounter which registers the number of pulses applied to its inputcircuit via channel 60a.

The control circuit 70, the subject of my copending application Ser. No.479,907, is programmed to energize the scanner electrodes, reset thecounter 65 and close the counter gate circuit 60 in response to anoperator command; to signal the counter gate. circuit 60 to open at thebeginning of an analytic run of scanning a metered volume of fluid; andto de-energize the scanner electrodes at the end of an analytic run.

Attention is now invited to the means for enabling the operator of theanalyzer to establish two separate threshold levels and to switch fromone to the other rapidly. The control knob of the switch 5-3 is shown atthe bottom of FIG. 2. It may be seen that the knob may be moved betweenthe two positions R and W. The potentiometer 47 has its slider driven bya control knob 200 mounted on the exterior of the panel of the housingfor the analyzer while the potentiometer 48 has a similar control knob202 which is similarly mounted. Each of these knobs has a scale alongits edge which cooperates with an index mark fixed to the panel as shownat 204 and 206 respectively. Each knob is locked into position, ifdesired, by means of a simple locking device shown at 208 and 210respectively. Also in FIG. 2 there is illustrated in somewhatdiagrammatic form the face of the cathode ray oscilloscope 35 which hasbeen broken into two parts to show two conditions of operation. Thecathode ray oscilloscope face is designated 212 and in order todistinguish between the two conditions, the left side is designated212-R and the right side is designated 212W. These two conditionsrepresent the re- 4 sponse of the analyzer to the two positions of theswitch S-3.

In counting and sizing blood cells, for example, the average volume ofthe red cells has been found to be on the order of cubic microns. Inorder to avoid the counting of debris and to prevent the inherent noiseof the circuit from causing spurious counts, the threshold level forcounting red blood cells should be set at a value which will pass onlythose particles whose volumes exceed 35 cubic microns. Therefore, theswitch S3 is set to the R position in which the potentiometer 47 isconnected into the detector circuit. The knob 200 is moved to the indexlocation designated as 35 cubic microns and locked in this position bythe locking device 208, potentiometer 49 and rheostat 50 having beenpreviously calibrated.

When a suspension of red blood cells is scanned by the fluid meteringapparatus 10, a trace similar to that shown at 212-R will appear on theface of the oscilloscope 35. The debris and noise is represented by whatis called hash :at the bottom of the trace as shown at 214. In the area216, the trace of the bottoms of the pulses will be dimly visible asthis represents pulse heights which are functions of particle sizesbelow 35 cubic microns. In the area 218, the trace of the-upper portionsof the pulses will be brightly visible as this represents pulse heightswhich are functions of particle sizes in excess of 35 microns. Thus thethreshold level, here 35 cubic microns in particle size, above whichparticles will be counted is visually distinguishable to the operator.

When white cells are to be counted, the control knob of switch 8-3 isplaced in the W position. The potentiometer 48 is now connected into thecircuit instead of the potentiometer 47. The knob 202 is rotated tobring any desired value of the threshold level calibrations to the indexmark 206. In FIG. 2 this value has been chosen as 50 cubic microns.

For counting white blood cells, the preferred threshold level representsa particle volume of 50 cubic microns since most of the cells have avolume in excess of 80 cubic microns.

When a suspension of white blood cells is scanned by the fluid meteringapparatus 10, a trace similar to that shown at 212-W will appear on theface of the oscilloscope 35. Most techniques for the counting and thesizing of white blood cells require the breaking down of the red bloodcells so that there is a substantially greater amount of debris than isfound present in red blood cell studies. The hash caused by this debrisis shown at 220. The dimly visible portions of the trace are designatedby the reference numeral 222 while the brightly visible portion of thetrace above the 50 cubic micron threshold level is designated by thereference numeral 224.

Where the apparatus of the invention is used primarily for the countingof two kinds of particles such as red and white blood cells, thecontinuously variable threshold level controls 200 and 202 may be presetand locked in place by the chief technician. After this, analytic runsmay be made by others of lower skill who may effect a change inthreshold level by merely operating the switch S-3. This provision notonly reduces the likelihood of making an erroneous analysis but providesmeans for reducing the time required to obtain a count. Since the fluidmetering apparatus 10 need not be servcied between analytic runs, itwill be appreciated that red and white blood cell determinations may bemade quickly :and in random order, the technician being required only tooperate the switch S3 to change the threshold level instead of adjustinga control knob such as 200. This arrangement also is suitable for use inother fields where different sizes of particles are studied.

It is believed that the invention is sufficiently described to enablethose skilled in the art to understand its structure, purpose and methodof operation. Obvious variations and changes in the circuitry andstructure, such as the use of transistors, are capable of being madewithout departing from the spirit or the scope of the invention asdefined in the claims. Y. 7 What it is desired'to claim by LettersPatent of the United States is:

1. In,- combination: i

a particle scanning apparatus generating a discrete signal for eachparticle scanned,

each said signal having a parameter which is a function of a physicalproperty of a respective scanned particle, and

a threshold detector circuit coupled to said scanning apparatus andreceiving each of said signals,

said detector circuit having a biasable detector portion coupled toreceive all of said signals,

said detector circuit also having a first and a second thresholddetermining means coupled to said de tector portion for at any one timebiasing said portion by a threshold level developed by either one ofsaid threshold determining means,

said first and second threshold determining means being electricallyparallel to one another and further comprising,

a common power source coupled to the parallel means,

and

said detector portion further having an output from which passes aresponse only to each said signal having said parameter of sufficientmagnitude to override the bias applied to said detector portion by saidone threshold means.

2. In a particle analyzing apparatus combining:

particle scanning means which generates scanning signals each having aparameter which is a function of a physical characteristic of arespective scanned particle,

threshold detector circuitry which receives all said scanning signalsbut transduces only those scanning signals which exceed a predeterminedthreshold level and thus represent scanned particles having a desiredphysical characteristic, and

means responsive to transduced signals for further aiding in theparticle analysis, the improvement residing in the threshold detectorcircuitry and comprising:

a unidirectionally conductive detector portion coupled to receivediscrete inputs representative of said scanning signals,

a plurality of biasing circuits each developing a discrete magnitude ofbias of finite difference, each said discrete bias having a magnitudesufficient to reverse bias said detector portion by a predeterminedthreshold level and block transduction of all scanning signals exceptthose whose representative discrete inputs are of a nature to overcomethe discrete bias and exceed the predetermined threshold level,

said biasing circuits being electrically and operationally independentfrom one another and being coupled in parallel through oppositeterminals of a common voltage source, and

selecting means coupled to said detector portion and discretelyconnectable to any one of said biasing circuits at any one time forpresenting to said detector portion one predetermined threshold level.

3. An improved threshold detector circuit for use with particleanalyzing apparatus and the like which generate a plurality of pulses ofdiffering amplitude which said threshold detector circuit receives andtransduces only said pulses having an amplitude in excess of apredetersaid bias circuits being similar to one another and containingmechanically variable impedance means,

said bias circuitsbeing electrically independent from one another duringoperation thereof, and

threshold bias selecting means connected between said detector portionand said bias circuits and at'any one time coupling any one of said biascircuits to said detector portion.

4. An improved threshold detector circuit as defined in claim 3 furthercomprising:

manually regulated means coupled to at least one of said mechanicallyvariable impedance means such that regulation thereof is mutuallyindependent of one another and said selecting means.

5. An improved threshold detector circuit for use with particleanalyzing apparatus and the like which generate a plurality of pulses ofdifi'ering amplitude which said threshold detector circuit receives andtransduces only said pulses having an amplitude in excess of apredeterminable threshold value comprising:

a biasable detector portion positioned to receive discrete signals ofvarying amplitude representative of each said pulse,

a plurality of bias circuits for applying to said detector portion aplurality of bias thresholds of predetermined values, and

threshold bias selecting means connected between said detector portionand said bias circuits and at any one time coupling any one of said biascircuits to said detector portion,

said detector portion having a pair of opposite ends, one of which isconnected to said selecting means, and further comprising,

a cathode follower circuit connected to the other end of said detectorportion,

said pulses being received by said cathode follower circuit whichgenerates and applies said signals to the other end of said detectorportion.

6. An improved threshold detector circuit as defined in claim 5 inwhich:

said detector portion comprises diode means poled for forward conductiontoward said one end thereof such that only signals received at saidother end thereof and of an amplitude in excess of the threshold valuebeing applied at that time are transduced.

7. An improved threshold detector circuit for use with particleanalyzing apparatus and the like which generate a plurality of pulses ofdiffering amplitude which said threshold detector circuit receives andtransduces only said pulses having an amplitude in excess of apredeterminable threshold value comprising:

a bisable detector portion positioned to receive discrete signals ofVarying amplitude representative of each said pulse,

a plurality of bias circuits for applying to said detector portion aplurality of bias thresholds of predetermined values,

said bias circuits being coupled in parallel to one another throughconnection with opposite terminals of a common voltage source,

said detector portion comprising electrically passive,

unidirectional conduction means, and

threshold bias selecting means connected between said detector portionand said bias circuits and at any one time coupling any one of said.bias circuits to said detector portion.

References Cited UNITED STATES PATENTS (Other references on followingpage) 7 OTHER REFERENCES Gucker et 1211., J. Colloid Science; vol. 4,1949 (QD 549.169), pp. 541560, Berg, Robert H., ASTM Special TechnicalPub. No. 234, 324-71PC; Symposium on Particle Size Measurement (TA406.7A5(1958), pp. 245-258. Published by the Amer. Soc. for "[restingMaterials, 1916 Race St., Philadelphia 3, Pa., presented at theSixty-First 8 Annual Meeting of the Amer. Soc. of Testing Materials,Boston, Mass, June 1958.

RUDOLPH V. ROLINEC, Primary Examiner.

WALTER L. CARLSON, Examiner.

C. F. ROBERTS, Assistant Examiner.

1. IN COMBINATION: A PARTICLE SCANNING APPARATUS GENERATING A DISCRETESIGNAL FOR EACH PARTICLE SCANNED, EACH SAID SIGNAL HAVING A PARAMETERWHICH IS A FUNCTION OF A PHYSICAL PROPERTY OF A RESPECTIVE SCANNEDPARTICLE, AND A THRESHOLD DETECTOR CIRCUIT COUPLED TO SAID SCANNINGAPPARATUS AND RECEIVING EACH OF SAID SIGNALS, SAID DETECTOR CIRCUITHAVING A BIASABLE DETECTOR PORTION COUPLED TO RECEIVE ALL OF SAIDSIGNALS, SAID DETECTOR CIRCUIT ALSO HAVING A FIRST AND A SECONDTHRESHOLD DETERMINING MEANS COUPLED TO SAID DETECTOR PORTION FOR AT ANYONE TIME BIASING SAID PORTION BY A THRESHOLD LEVEL DEVELOPED BY EITHERONE OF SAID THRESHOLD DETERMINING MEANS, SAID FIRST AND SECOND THRESHOLDDETERMINING MEANS BEING ELECTRICALLY PARALLEL TO ONE ANOTHER AND FURTHERCOMPRISING, A COMMON POWER SOURCE COUPLED TO THE PARALLEL MEANS, ANDSAID DETECTOR PORTION FURTHER HAVING AN OUTPUT FROM WHICH PASSES ARESPONSE ONLY TO EACH SAID SIGNAL HAVING SAID PARAMETER OF SUFFICIENTMAGNITUDE TO OVERRIDE THE BIAS APPLIED TO SAID DETECTOR PORTION BY SAIDONE THRESHOLD MEANS.